Structure for large diameter grinding mill



Aug. 6, 1968 "r. E. HARRIS 3,395,869

STRUCTURE FOR LARGE DIAMETER GRINDING MILL Filed Feb. 25, 1965 5 Sheets-Sheet l THOMAS E. HARRIS Y w Da /9P ATTORNEYS INVENTOR 6, 1968 T. E. HARRIS 3,395,869

STRUCTURE FOR LARGE DIAMETER GRINDING MILL Filed Feb. 25, 1965 5 Sheets-Sheet 2 FIG. 3

FIG. 4

INVENTOR THOMAS E. HARRIS BY 9 W D ATTORNEYS Aug. 6, 1968 T. E. HARRIS 3,395,369

STRUCTURE FOR LARGE DIAMETER GRINDING MILL Filed Feb. 25, 1965 3 Sheets-Sheet 5 INVENTOR THOMAS E. HARRIS BY Z$9QQQ Z Qa7/91 I ATTORNEYS United States Patent 3,395,869 STRUCTURE FOR LARGE DIAMETER GRINDING MILL Thomas E. Harris, Valois, Quebec, Canada, assignor to Dominion Engineering Works, Ltd'., Montreal, Quebec,

Canada Filed Feb. 25, 1965, Ser. No. 435,228 5 Claims. (Cl. 241-176) ABSTRACT OF THE DISCLOSURE An improved drum structure for a rotary grinding mill includes spoke-like load transfer members external to the drum connecting the drum outer peripheral edges with the mill trunnions substantially independently of the drum heads, to reduce working stresses on the heads.

This invention relates to rotary, rod, ball, pebble or autogenous grinding mills and more particularly to a new and improved construction of such mills which permits the manufacture of larger mills on more economical basis than has hitherto been possible.

Rotary grinding mills are utilized extensively in the mining industry for the reduction of friable ore. Mills of this type grind or comminute friable ore to a specific mesh size by enclosing the ore in a cylinder which is rotated at a constant predetermined speed by means of an electric motor. Rods or balls may be enclosed with the ore to provide a reducing medium or the ore itself may be used as a self reducing medium. The tumbling action imparted to the ore within the cylinder, causes the ore to be ground or comminuted, and, on reaching the desired mesh size, the ground ore is discharged from the mill.

Mills of this type generally comprise three major components: .A rolled plate steel cylindrical shell and two heads. The shell and heads which in combination form a rotatable hollow drum structure, will be defined hereafter for conciseness as the drum. The heads may be one piece castings, fabrications, or castings and fabrica tions in combination. The heads are attached to the cylindrical shell to make up the rotating mill drum structure and the central portion of the heads extend outwardly to form hollow bearing trunnions.

Large mills of this type are expensive, difficult to transport and difiicu'lt and expensive to assemble. However, from the point of view of efficiency of operation it is desirable to construct such mills, particularly autogenous mills, of large diameter. It can be readily appreciated that the larger the diameter of the mill the more significant becomes the above mentioned disadvantages.

It is thus an object of the present invention to provide a novel construction for a rotary-grinding mill which will permit such mills to be made of large diameter for maximum efliciency in operation and which overcome the disadvantages inherent in conventional rotary-grinding mills of large diameter. According to the present invention, the drum of the rotary grinding mill may be constructed of relatively thin sheet metal fabrications: Rod-like structural elements extend between spaced pheripheral points on each side of the drum to anchor rings which are disposed on each bearing trunnion at a point spaced outwardly from the points of connection between the drum and the bearing trunnions. These rod-like structural elements permit the transmission of the tension and compression forces directly from the drum and the bearing trunnions. Thus, the difiiculties inherent in prior art rotary-grinding mills are completely overcome in that it is unnecessary to utilize heavy castings for the heads, and, mills constructed according to the present invention can be readily dismantled, transported and assembled.

The primary object of the present invention is to provide a rotary-grinding mill with rod-like structural elements which transmit the tension and compression forces which emanate from the rotating drum to the bearing trunnions.

Another object of the present invention is to provide a novel structure for grinding mills wherein the rotating drum may be manufactured or constructed from relatively thin material thereby permitting the construction of rotary mills in larger diameters than has been hitherto possible.

Another object of the present invention is to provide a structure for a rotary grinding mill whereby the overall diameter of the mill may be substantially increased and the mill may be made in a more economical manner than is possible with conventional mill construction.

Still another object of the present invention is to provide a structure for large diameter rotary grinding mills in which the individual components, which comprise the rotating drum assembly, are constructed in smaller sections than conventional mills for ease of manufacture, erection, dismantling and transportation.

Other objects and many of the attendant advantages of the present invention will become more readily apparent upon consideration of the following detailed specification when considered in connection with the accompanying drawings wherein:

FIGURE 1 is a perspective view, partly in section, of an autogenous grinding mill embodying the present invention.

FIGURE 2 is a sectional elevation of another embodiment of the present invention and also represents a simplified force diagram.

FtIGURE 3, is a view partly in section, of a portion of the trunnion and the shell of a typical grinding mill and shows details of one method of attaching the tension/ compression members.

FIGURE 4 is an end view along the lines 4-4 of FIGURE 3, and

FIGURE 5 is a sectional elevation of a further embodiment of the invention.

Convention-a1 grinding mills of the type referred to herein usually comprise a cylindrical shell and axi-symmetric heads which extend outwardly from the shell to form bearing trunnions. A mill of this general type is shown in US. Patent 3,010,661. The drum heads may be made of single castings or ribbed platework fabrications and it can be appreciated that it is necessary to construct the entire drum assembly of relatively thick metal in order to withstand the high compression and tension forces exerted thereon during operation of the mill. The triangular shaped ribs which are shown in the above referenced patent and which are used conventionally in the art do not provide a solution to the problem which the present invention overcomes. The rib structures may be subjected to high tension or compression forces depending on the position of the ribs relative to the axis of rotation along the outer face thereof, while the inner portion of the rib and the head to which it is attached is also subjected to high stresses. Thus the ribs must be made of relatively heavy metal and are generally cast in a single piece with the heads or alternatively, the ribs are welded to the heads.

In FIGURE 1 there is shown a cylindrical shell 10 having cylinder heads shown at 20 and 21, which cylinder heads are constructed of relatively thin section plate steel fabrications and are capable of being disassembled for ease of shipping. The means interconnecting the discs 20 and 21 With the outer shell 10 are not specifically shown as they form no part of the present invention and any conventional means may be used for this purpose. A plurality of compression and tension members such as rods 22 are connected at spaced points to the edge 23 of shell by means of brackets 25. The other ends of members 22 are secured to an anchor ring 26 which is rigidly attached to the bearing trunnion 14. The bearing trunnion 14 is journalled in pedestal mounted bearing 16 and is provided with a trunnion mounted gear 17 which is operatively associated with an electric motor for driving the cylinder.

In the embodiment shown in FIGURE 1 the tension and compression members 22 are shown as tubular in cross-section for strength and lightness but obviously these members may be made solid and need not be cylindrical in shape. It is also readily apparent that the construction of the mill on the opposite side of the cylindrical shell not visible in FIGURE 1, is identical to that part shown, although the geometric configuration or arrangement of members 22 may be varied if desired.

The function of members 22 depends upon the specific location of each member with respect to the mill axis. For example, the member 22 extending upwardly from the axis as shown in FIGURE 1 will be in compression while the diametrically opposed member 22 will be in tension. All of the other members 22 will be in compression and tension by decreasing amounts depending on their relative location from the vertical position. Each member 22, is in turn subjected to cyclic load variations as the mill is rotated. These cyclic load variations are shared between the members 22 which are seen in FIG- URE 3 and those members 22 which are axially opposed therefrom.

In FIGURE 2 there is shown a force diagram which illlustrates schematically how the various forces emanating from the mill structure and from the ore being tumbled within the mill are transmitted to the members 22. In FIGURE 2 the shell 10 and annular discs 20 and 21 are analagous to those structures shown in FIG- URE 1. If a force -F is applied to the bottom member BC, it is transmitted to B and C in equal proportions assuming symmetry and it can be shown that there are resultant tension forces in B] and tension or compression forces in BY. Furthermore, it can be shown that in this structure no moments exist at any of the connections of members 22 to the other components of the mill structure.

FIGURE 2 also illustrates schematically an alternative structure from that shown in FIGURE 1, in that a plurality of radially disposed tubular compression and tension members 27 and a plurality of horizontal struts 28 corresponding in number to members 27 in combination with members 22 form a cage in which elements 10, 20 and 21 may be secured such that members DX, ES, BY and CU act as alternatives to members 20 and 21 with respect to the transmission of forces.

Referring now to FIGURES 3 and 4, these show details of the preferred form of attaching the tension and compression members 22 to the shell and trunnion of the mill. The attachment of only one member to the mill structure is shown but it is readily apparent that all of the members will be attached in a similar manner.

Rigidly attached within the bore of member 22 is an insert 29 and this insert has an extension 30 with a male thread thereon. A hole or slot 31 in bracket receives the extension and nuts 32 and 32a on opposite sides of the bracket 25 retain member 22 in the desired position. Spherical washers 33, 34, 35, and 36 permit accurate alignment with respect to bracket 25. At the opposite end of member 22 remote from extension 30 is secured a flange 37. The flange 37 is provided with holes 38 and 39 to permit the insertion of bolts 40 and 41 into threaded holes 42 and 43 in the anchor ring 26.

In FIGURE 5 there is shown a further embodiment of the invention which is similar to the FIGURE 2 embodiment in that there are provided a plurality of horizontal struts 50, radial compression and tension members 51, and members 52, which form a cage supporting the drum. The drum has side walls 53 which include angular inwardly extending portions 54. This construction of the side walls provides for a better mixing action of the ore within the mill.

It is readily apparent from the foregoing description that the present invention provides means for constructing a grinding mill wherein a large diameter mill may be fabricated from relatively thin plate metal and wherein the tension and compression forces developed within a drum shaped grinding mill are transmitted to the bearing trunnions by means of rod-like members interconnecting spaced peripheral points on the drum to an anchor ring mounted on the trunnion.

Obviously many modifications and variations of the present invention are possible in light of the above teaching. What is new and desired to be secured by Letters Patent is:

I claim:

1. In a rotary grinding mill comprising a rotatable drum having a cylindrical shell with axially opposed drum heads attached thereto, the improvement comprising a plurality of rod members substantially separate from said heads extending inwardly to connect the ends of the drum adjacent the outer periphery thereof with drum supporting trunnion means, in load transfer relation therewith, to maintain the trunnions in substantially co-axial relation with the drum whereby in operation at least a portion of the working load acting on said shell is transferred to said trunnion means substantially independently of said drum heads.

2. A grinding mill as claimed in claim 1 wherein the radially inner ends of said rods at each end of said drum are attached to an anchor ring of the respective said trunnion means.

3. The grinding mill as claimed in claim 2 wherein said rods are arranged externally of said drum in symmetrical arrangement about the axis of rotation of said drum, extending radially outwardly from said anchor rings in inclined relation to the outer edge portion of said drum.

4. The grinding mill as claimed in claim 1 wherein the radially outer ends of said rods are connected with axial end portions of said shell.

5. The grinding mill as claimed in claim 1 wherein the radially outer ends of said rods are connected with radially outer portions of said drum heads.

References Cited UNITED STATES PATENTS 2,451,708 10/1948 Arpin 24l177 FOREIGN PATENTS 378,025 7/1923 Germany. 583,002 8/1933 Germany.

GERALD A. DOSI, Primary Examiner. 

